A geometry kernel is a big thing. It’s a huge thing. Maybe even big enough to see from space. By most accounts, even the Great Wall of China is not visible from space. However, other huge infrastructure is: highways, airports, bridges, and dams. This is the scale for this post. Decades of work, in a five topic flyover.
1. Creating 3D models
If you asked a guy on the street what a geometry kernel was for, odds are he’d reply "creating 3D models". Most 3D ACIS Modeler enabled applications create 3D models. And if you’ve read this far, you’ve probably created a 3D model at some point in your life. The basic steps haven’t changed a lot in the last 25 years.
Sketching is the process used to create a collection of curves, circles, ellipses, lines, and B-splines. Sketching is just connecting the dots, users input points and tangents, then applying constraints on a 2D grid. The collection of curves matches part of a design, or makes one up.
Curves can create surfaces by extruding, revolving, sweeping, or skinning. Surfaces can be trimmed and stitched to create solids.
The construction of primitive solids follows from specific parameters. This may include solids such as spheres, tori, cuboids, etc.
Finally, overlapping simple solids can be combined with Boolean operations like union and subtract to make a complex 3D model. In 3D ACIS Modeler, 3D models can also be non-manifold, combining solids, two sided sheet bodies and wires.
While all the above is standard fare for a geometry kernel, creating stable, fast high-level APIs for a geometry kernel is no small feat. One of the training exercises at Spatial for new 3D ACIS Modeler developers is writing a function to create a solid tetrahedron using low-level interfaces. It’s surprisingly hard - try for yourself.
I cover the other 4 essentials in my eBook. Please click below to download.
